Which is preferred for spirited street applications ?

Discus any logic that may apply, please....


Dimpled, is newer technology but drilled actually seems it would do more for cooling.

But, being drilled MAY be a bit weaker...given the same metalurgy

 

Neither. Dimpled/drilled are pure 'bling' for street driven cars, nothing to do with better stopping.

 

I agree, I doubt you will notice any difference, some people complain about noise from drilled/dimpled discs.
There was a theory at one time that depending on disc thickness and hole diameter you could increase the surface are by drilling and improve cooling, but vented discs have made that an obsolete notion.

 

Drilling/dimpling/slots DECREASE friction area, the exact opposite of what's needed to stop a car. If our brakes ever got hot enough to induce the much feared pad 'outgassing', the loss of friction area to get rid of the vapours might be the lesser of two evils. But they don't.

 

Yes indeed but I was referring to surface area which potentially could be increased.(I didn't say it would be useful)

The earliest use of drilled discs that I recall in general use was on 1970's motorcycles that used stainless discs that didn't work in the wet.

 

Not sure how drilling holes could increase surface area?

I well remember ineffective disk brakes on bikes. My first new m/c was a '73 Norton Commando Roadster. Terrifying in the wet unless stops were well anticipated and compensated for.

 

If you have a 10mm thick disc you will have removed a total of 56.54 sq mm from the disc face but have created 188.49 of surface area inside the hole.

I drilled the Dunstall twin discs on my Commando but only because it looked good.

 

I believe that the confusion is in that you are referring to "surface area with the air", while others were thinking in terms of "surface area in contact with the pads".

 

I did say the idea was to improve cooling not stopping.

 

For what it's worth I fitted grooved and dimpled discs to front and rear. The brake performance and longevity seems much better than with the old standard discs, I suffer with far less brake fade and it feels to haul up a little sharper.
There is some noise with them, but it's a nice fluttering sound which I quite like, there's a re assuring hum when braking hard from high speed.
I wouldn't go back to standard discs.

 

Yup, following you now. Sometimes I'm a little, you know.

 

Whenever I check my drilled Brembo discs, most of the holes are blocked with brake dust.

Not convinced drilled does anything for stopping efficiency on a street vehicle.

Graham

 

Graham
You've mentioned that before. What type of pads are you running? I've got the original Brembos and discs they are very dirty ( very heavy brake dust), but I've never had a blocked hole. the hole stay clear..

 

The car was serviced by the same original Jaguar Dealer from new and pads were changed by them before I collected the car.

Jaguar Dealers here can't use anything but Jaguar parts so they are MXD1550AB (Brembo in a Jaguar box).

Dust on the wheels isn't particularly heavy (although Sepangs aren't the easiest to keep clean) and I only found out the holes were blocked when I tried putting a small drill bit through them. The discs themselves stay bright.

Graham

 

Graham
After reading your last post I went out and with my pen light and checked holes in the rotors, their clean. I have the same pads that you do MXD 1550AB. Possibly the difference is I don't get stuck in the rain much, while you guys over the pond don't get out of the rain to often. I do power wash my wheels and brakes a couple of times a year. It's a lot easier to get to the rotors and calipers with the Detroit wheels. The brake dust is one of the biggest reasons I wash my car. After a couple of hours of driving the hills put your hand on the quarter and it will be black with a fine dust.

 

That was a bit below the belt Doug!

 

But nevertheless, absolutely true.
Graham

 

I'm not trying to hit below the belt, but every time you photograph a car in England it's raining, or every episode of Wheeler Dealer, or Top Gear, Old British War Movies. I've got to quit rambling.

 

Just an observance, the purpose of the holes is better cooling and off-gassing of tortured brake pads. Slots are to cut away the surface of the pads to expose new pad surface. Neither help normal braking and actually slightly decrease contact area, ergo somewhat reduced braking. If you use your brakes hard, like slowing from 150 to take the apex at 50 over and over, yeah, they have a place.

 

I've read a Synopsis of the SAE test of Cross drilled verses non drilled. For street use cross drilled has been proven to out perform you non drilled disc. below is the web site to read the whole Synopsis.
http://www.tazcobra.com/SAE_2006010691_Synopsis.pdf

These test were conducted by the Society of Automotive Engineers, It is one of the reason why many performance cars come with cross drilled.